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首页> 外文期刊>Journal of structural geology >Recognizing the seismic cycle along ancient faults: CO_2-induced fluidization of breccias in the footwall of a sealing low-angle normal fault
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Recognizing the seismic cycle along ancient faults: CO_2-induced fluidization of breccias in the footwall of a sealing low-angle normal fault

机译：认识古代断层的地震循环：CO_2诱导的低角度正断层断层下盘角砾岩的流化

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摘要

The Zuccale low-angle normal fault exposed on the island of Elba, Italy, is a crustal-scale structure which contains a strongly foliated fault core. In the immediate footwall of the Zuccale fault, cohesive fault-related breccias which were initially deformed by typical frictional deformation mechanisms experienced fluidization over areas of at least 10~(-2)-10~(-3) km~2. Three internal variants of fluidized breccia are recognized, with each related to a separate fluidization event. Characteristics of the fluidized breccias include: (1) a highly irregular 'intrusive' boundary with the overlying fault core; (2) no grain-scale evidence for typical frictional deformation mechanisms; (3) an association with carbonate cements indicating that fluids contained CO_2; and (4) a clast-preferred orientation suggesting that fluids were moving vertically and spreading laterally as they encountered the foliated fault core. Our observations suggest that the fluidized breccias are representative of the interseismic period along the Zuccale low-angle fault, and developed across small fault patches during build-ups in fluid overpressure. Attainment of a critical fluid overpressure triggered embrittlement and the formation of low-angle slip surfaces and sub-vertical tensile veins within the overlying fault core, which may account for the presence and the dimensions (10~(-1)-10~(-3)km~2) of rupture surfaces which produce microseismicity along active low-angle normal faults in central Italy.
机译：在意大利厄尔巴岛上裸露的祖卡勒低角度正断层是一个地壳尺度的结构，其中包含一个强烈的叶状断层。在祖卡勒断层的直接下盘壁，与粘性断层有关的角砾岩最初通过典型的摩擦变形机制变形，在至少10〜（-2）-10〜（-3）km〜2的区域内经历了流化作用。识别出流态角砾岩的三个内部变体，每个变体与单独的流化事件有关。流化角砾岩的特征包括：（1）与上覆断层核心高度不规则的“侵入”边界； （2）没有典型摩擦变形机理的晶粒度证据； （3）与碳酸盐水泥的联系，表明流体中含有CO_2； （4）最优先的取向表明流体在遇到叶状断层岩心时是垂直运动并横向扩散的。我们的观察结果表明，流化角砾岩代表着Zuccale低角断层的间震期，并在流体超压形成期间跨小断层斑块发育。达到临界流体超压会触发脆性，并在上覆断层岩心内形成低角度滑动面和亚垂直张应力脉，这可能解释了其存在和尺寸（10〜（-1）-10〜（- 3）km〜2）的破裂面，沿意大利中部活动的低角度正断层产生微地震。

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